1. Field of the Invention
This invention relates to optical elements having a pair of transparent parallel flat plates with their intervening space having an optically transparent substance sealed therein, wherein the optical performance of a light beam passing through the plates is made to arbitrarily vary by varying the relative angle of one plate to the other plate. The invention also relates to a method of manufacturing the same and, more particularly to such an optical element which is suited to be used in a photographic system of, for example, a photographic camera, video camera, etc. as arranged in a portion of the photographic system to form an image stabilization optical system for compensating for the shake of an image due to the vibration of the photographic system.
2. Description of the Related Art
It has been known that an optically transparent substance, for example, liquid or silicone rubber, is sealed in between two transparent parallel flat plates to form a variable-angle prism body, and, as it is used as an optical element, when the angle (or the degree of parallelity) of one of the two plates to the other varies from outside control, a light beam passing through the plates provides a desired variation in optical performance. There have been many previous proposals for such an optical element.
FIG. 1 and FIG. 2 are schematic sectional views of an optical element of the sort proposed in, for example, Japanese Patent Publication No. Sho 41-11906. The optical element shown in these figures is constructed in such a way that two transparent parallel flat plates 201 are positioned in spaced surface-to-surface relation, a flexible member 202 for connection of these members encloses a space, and transparent liquid is sealed in this space. As a result, incident light rays h are made to deflect to a predetermined angle when emerging therefrom.
FIG. 3 and FIG. 4 are schematic views of another optical element which is proposed as an example of an embodiment in Japanese Laid-Open Patent Application No. Sho 60-176017. The optical element shown in these figures is constructed in such a way that two transparent parallel flat plates 221 are positioned in spaced surface-to-surface relation, and a transparent elastic body 224 is sandwiched between these plates. Further, similar to FIGS. 1 and 2, incident light rays h are made to deflect to a predetermined angle when emerging therefrom. Any of the conventional optical elements is operated in such a manner that a force from the outside is applied to vary the angle which one of the two flat plates makes with the other so that a variable angle prism whose vertex angle can be arbitrarily controlled is formed, permitting the incident light rays to emerge with a predetermined angle of deflection.
Since the connection member of the conventional optical element is, however, made of such a material and formed to such a shape that it expands or contracts when the angle which the two flat plates make with each other varies, the required driving power for this is generally large. For this reason, the drive source is necessarily of large size, and, as the number of repetitions of deformation increases, an accident such as break in the connection member is liable to occur.
Furthermore the substance sandwiched between the two parallel flat plates, as compressed, permeates through the connection member, or oozes out past the weld joint of the connection member with the parallel flat plates, and, particularly in the case of the transparent elastic substance, as it absorbs moisture in the air, its refractive index is caused to fluctuate.
Besides these, there is another problem in that the driving of the optical element accumulates stress at the joint of the connection member with the parallel flat plates, causing the joint to be peeled off and the interior substance to ooze out.